Farnesoid X receptor (FXR, NRIH4),1 a member of the bile acid nuclear hormone receptor superfamily, is a ligand-dependent transcription factor that regulates gene networks involved in regulating lipid and cholesterol homeostasis.2 FXR is expressed primarily in tissues exposed to high concentrations of bile acids, such as the intestine, kidney, adrenal gland, and liver.3 Consistent with the role of FXR, bile acids are the primary activating endogenous ligands of FXR.3-4 As the bile acid sensor, FXR regulates the expression of transporters and biosynthetic enzymes crucial for the physiological maintenance of bile acid homeostasis.